1. Field of the Invention
The present invention relates to communication in a wireless environment. More particularly, the invention relates to systems and methods for setting up a push-to-talk group call in a wireless communications system.
2. Background
A push-to-talk (PTT) call in a group communications system allows multiple users in different locations to simultaneously communicate. Group communications systems are often used by businesses (e.g., fleets of taxis, buses and trucks, construction crews, etc.) and governmental authorities (e.g., police and law enforcement agencies, fire departments, military users, forest firefighters, etc.). During a push-to-talk call, one user, for example, a taxi cab dispatcher, can simultaneously transmit to the remaining members of the group. The user who initiates the group communication is sometimes called an originator. In some implementations the originator controls which user has the floor to transmit while all other users listen. In other implementations the group communications system is organized in a less centralized manner, so that different members of the group take turns transmitting while all the other members listen. In either case, when the originator begins the process of making a group communication, the call must first be set up within the group communication system to allow all participating users to transmit and receive signals, including control signals for the call.
Push-to-talk group calls between several users are often implemented using Internet Protocol (IP) based schemes. Examples of such IP schemes include the Q-Chat Signaling Protocol (QSP) as the Session Initiation Protocol (SIP). A push-to-talk call between several users tends to take a lot longer to set up than a regular call between two parties. When an originator of a PTT call decides to place a group call, the originator selects a number of target users to participate in the group call and presses the PTT button. The originator must wait until the floor is granted before beginning the group call. In conventional group communication systems there is a considerable delay from the time the originator pushes the PTT button to when the floor is granted to start the PTT group call. This latency period is due to several tasks which must be performed in completing the group call. One of the tasks in setting up a group call involves the collection of the various target users' information, and then packaging a call message in the form of a data packet. What is needed is a group communication system which incurs less latency in setting up a group PTT call.